The present invention relates to an intake manifold, for example, for use with motor vehicle engines.
The term "aluminum" as used herein and in the claims includes pure aluminum and aluminum alloys. The term "wrought aluminum" as used herein and in the claims refers to an article of aluminum prepared by extrusion, impact extrusion, forging or like plastic working process. Further the term "center line average height" is used herein and in the claims according to the definition of JIS B0601-1982.
For example, motor vehicle engines have recently been proposed which have two intake ports formed for each of its cylinders and each provided with a valve to achieve improved performance. In the high speed range of engine rotation, air or fuel-air mixture is supplied to the two intake ports provided for each cylinder, while in the low-to-medium speed range of rotation, air or fuel-air mixture is supplied to only one of the two intake ports so as to obtain a high output and high torque in the high speed range and to obtain a high output and high torque in the low-to-medium speed range.
For such engines, an intake manifold has heretofore been used which is made of a casting in its entirety and which comprises a plenum chamber and branches connected to the respective intake ports.
For the engine to give a high output and high torque especially in the low-to-medium speed range, it is desired that the branch channel connected to the intake port to which air or fuel-air mixture is supplied in both the high speed range and the low-to-medium speed range be larger in length and smaller in cross sectional area than the branch channel connected to the other intake port to which air or fuel-air mixture is supplied only in the high speed range so as to introduce air or fuel-air mixture into the cylinder at an increased flow velocity in the low-to-medium speed range.
In the case of the cast intake manifold, however, it is difficult to design the two branch channels with such lengths and cross sectional areas a to give an ideal flow velocity to the air or fuel-air mixture. In fact, this is impossible if the engine has many cylinders. The reason is that although the intake manifold needs to be compact because the space available for the motor vehicle engine room is limited, the cast intake manifold fails to fulfill the requirement when so sized as to be accommodated in the engine room.
Moreover, the cast intake manifold has the problem of increased weight since the thickness of the peripheral wall can not be reduced beyond a certain limit in view of the flowability of the molten metal to be cast. The casting is rough-surfaced, has voids and must therefore be internally smooth-surfaced by finishing to ensure reduced air resistance for an improved intake efficiency. Thus, the cast manifold has the problem of necessitating a cumbersome finishing. procedure. Nevertheless, it is impossible to finish the entire inner surface of the intake manifold in view of its configuration and accordingly to fully reduce the air resistance for an improved intake efficiency.